Construction for end of cable sheath and method of welding sheath

ABSTRACT

This application for welding an oil impermeable sheath of a high voltage power cable uses a tube inserted into the clearance between the core and the sheath of the cable to shut off oil circulation through this clearance immediately inside the sheath. The tube extends beyond the end of the sheath and oil flows from the end of the cable during the welding operation even though the space within the sheath immediately under the region of welding is free of oil. The sheath can be welded to a joint housing without oil contamination of the weld and the invention prevents vaporization of oil and possible blow-out of near molten areas of the sheath adjacent to the weld.

Dima et al.

May 8, 1973 CONSTRUCTION FOR END OF CABLE SHEATII AND METHOD OF WELDINGSHEATH Inventors: Attila Dima, Piscataway; George S. Eager, Jr., UpperMontclair, both of NJ.

General Cable Corproation, New York,N.Y.

Filed: Sept. 2, 1971 Appl. No.: 177,383

Assignee:

US. Cl. ..174/10, 29/628, 29/630 F, 174/20, 174/22 R Int. Cl. ..H02g15/20, H02g ll] 4 Field of Search ..l74/8, 10, 2O, 21 R, 174/22 R, 22 C,23 R; 29/628, 630 F, 203

References Cited UNITED STATES PATENTS 2/1933 Eby ..174/1OUX 9/1936Phillips ..l74/21R FOREIGN PATENTS OR APPLICATIONS 386,093 H1933 GreatBritain ..l74/10 525,637 9/1940 Great Britain ..174/21 R 547,617 9/1942Great Britain ..1 74/22 R Primary ExaminerLaramie E. AskinAttorney-Nichol M. Sandoe et a1.

[5 7] ABSTRACT This application for welding an oil impermeable sheath ofa high voltage power cable uses a tube inserted into the clearancebetween the core and the sheath of the cable to shut off oil circulationthrough this clearance immediately inside the sheath. The tube extendsbeyond the end of the sheath and oil flows from the end of the cableduring the welding operation even though the space within the sheathimmediately under the region of welding is free of oil. The sheath canbe welded to a joint housing without oil contamination of the weld andthe invention prevents vaporization of oil and possible blow-out of nearmoltenareas of the sheath adjacent to the weld.

10 Claims, 5 Drawing Figures RESERVOIR Pmmwm' 8I973 531732352 OILRESERVOIR ATTORNEYS.

CONSTRUCTION FOR END OF CABLE SHEATH AND METHOD OF WELDING SHEATHBACKGROUND AND SUMMARY OF THE INVENTION High voltage power cablesinsulated with paper or synthetic tapes and oil may be installed in pipeunder oil pressure, or without pipe, if it is manufactured with an oilimpermeable sheath. There are many different types of sheathingmaterial, e.g., lead, aluminum, steel etc.

It is a common practice to make a hermetic connection between a metallicoil impermeable cable sheath and a joint housing by a solder-wipe. Whenother metallic materials than lead are used for cable sheathing, awelded connection may be mechanically more advantageous and reliablethan a solder wipe connection or even a mechanical seal.

Great care is needed to protect a cable sheath and a joint housing fromoil contamination in the area to be welded.

An oil barrier is needed inside of the cable sheath to divert the oilfrom the very hot part of the metallic cable sheath during the weldingprocess. If the oil is in contact with the inside wall of the nearlymolten metallic cable sheath, the oil will evaporate and produce a vaporpressure which may blow a hole in the almost molten cable sheath.

This invention provides a temporary oil barrier which is used to keepthe oil out of the welded section during the welding. This barrierconsists of a tube preferably of metal having good thermal conductanceand a cylindrical seal made of a heat resistant elastomer. When the tubeis pushed into the cable sheath, the cylindrical seal is pressed againstthe inside wall of the cable sheath and keeps the oil out of the hightemperature area during the weld. The oil can freely circulate inside ofthe tube. Since the tube has a good heat conductance, it protects thecable insulation against the excessive heat produced by welding.

Other objects, features and advantages of the invention will appear orbe pointed out as the description proceeds.

BRIEF DESCRIPTION OF THE DRAWING In the drawing, forming a part hereof,in which like reference characters indicate corresponding parts in allof the views;

FIG. 1 is a sectional view, partly broken away, showing the sealingmeans of this invention assembled with a cable and sheath and showingthe end portion of a joint housing welded to the cable sheath;

FIG. 2 is an isometric view of the tube shown in FIG.

FIG. 3 is an isometric view of the elastomer sealing means which islocated around the ridge on the tube in FIG. I; and

FIGS. 4 and 5 are enlarged sectional views taken on lines 4--4 and 55,respectively, of FIG. 1.

DESCRIPTION OF PREFERRED EMBODIMENT FIG. 1 shows a high voltage electriccable which includes a conductor 12 (FIGS. 4 8c 5), shown as stranded,surrounded by a semi-conducting conductor shielding 14. There is oilfilled insulation 16 which may be paper or a porous plastic tape such asspunbonded polyethylene surrounding the core shield 14.

A semi-conducting insulation shielding 20 surrounds the insulation 16and the outside of the cable is enclosed by an electrostatic shield 22which is corrugated in cables of large size to increase the flexibilityof the cable. This sheath 22 is made of metal. Lead was formerly incommon use but cable sheaths are now made more often of aluminum orsteel. The clearance between the cable sheath 22 and the cable coresurrounded by the insulation shielding 20 is filled with oil of the samekind as used in the insulation 16 and this oil is indicated in FIG. 1 bythe reference character 24.

The oil 24 is maintained under some pressure so that no air can enterthe cable sheath. In FIG. 1 the sheath 22 is shown diagrammaticallyconnected with an oil supply reservoir 26 from which oil is drawn by apump 28 and discharged into the cable sheath and cable through tubing30. The pump 28 is shown as driven by an electric motor 32. Thisapparatus is merely representative of means for maintaining theclearance in the sheath and the insulation of the cable supplied withoil under pressure which is somewhat higher than atmospheric pressure.

FIG. 1 shows a portion of a joint housing 36 which has a neck 38 thatsurrounds an end portion of the sheath 22. The joint housing 36 isconnected to the sheath 22 by a fused connection such as a welded connection 40.

In FIG. 1 the sheath 22 is shown as corrugated except at the end portionwhich is left with a cylindrical shape. If the sheath is corrugated allthe way to the end, as will occur if the sheath has been cut from alonger length of cable, then the corrugations must be pressed out or theapparatus of this invention must be of a size to fit within the minimumdiameter of circumferentially extending corrugations.

In order to insurethat no air can enter the cable during the connectingof the joint housing 36 to the sheath 22, it is necessary to maintainoil circulation through the cable during the welding of the housing tothe sheath. This has presented problems in the prior art. One problem isoil contamination caused by oil flowing from the open end of the sheathand spreading over the outside of the sheath in the vicinity where theweld is to be made. Another problem is that if there is oil in contactwith the shea'th at the location where the weld is being made, the heatof the weld may be sufficient to evaporate the oil and cause vaporpressure within the sheath that sometimes blows a hole through thesheath at the region where the metal of the sheath is highly heated andnearly molten and therefore of very little tensile strength.

This invention includes a stifi metal sleeve 44 which fits loosely overthe cable core with some clearance between the inside surface of thetube 44 and the outside surface of the insulation shielding 20 whichcomprises the circumference of the cable core.

This tube 44 has a circumferential ridge 46 which is steep on one sidebut shaped to provide a wedge surface 48 on the other side of the ridgetoward the inner end of the tube 44.

A washer consisting of a cylindrical sealing element 50 made of a heatresistant elastomer is forced over the inner end of the tube 44 andupward along the wedge surface 48 as shown in FIG. 1. This cylindricalsealing element 50 may be made of silicone rubber, neoprene, or otherheat resistant elastomers.

The maximum diameter of the ridge 46 is preferably slightly less thanthe inside diameter of the sheath 22. The sealing element 50 is pushedupward along. the wedge surface 48, with resulting stretching of theelastomer, until the outer end of the sealing element 50 extendsslightly beyond the circumference of the ridge 46 at the maximumdiameter of the ridge. The tube 44 is then placed over the core of thecable and is pushed into the cable sheath 22 as shown in FIG. 1. Thetube 44 is forced along the inside of the cable sheath in the clearancebetween the core and the cable sheath until the ridge 46 and the sealingelement 50 reach a location beyond that where the weld 40 is to belocated.

The wedge surface 48 compresses the sealing element 50 into firm contactwith the inside surface of the cable sheath 22 so that none of the oil24 can escape through the clearance between the cable sheath 22 and thetube 44. There is, however, sufficient clearance between the insidesurface of the tube 44 and the cable core to permit circulation of oilthrough the cable and some oil discharges from the end of the tube 44around the cable core but at a distance safely removed from the regionof the weld so that there is no danger of this oil coming in contactwith the cable sheath 22 or getting on the outside of the sheath at alocation where the oil could contaminate the weld.

Because of the fact that the tube 44 is pushed into the cable sheath farenough to seal off the oil 24 at a location ahead of the region wherethe weld 40 is located, there is no oil in contact with the portion ofthe sheath 22 which is highly heated during the welding operation. Thusthere can be no vaporization of oil in the sheath or pressure exerted bysuch vapor against the portions of the sheath that are highly heated andnearly molten during the welding operation.

The tube 44 is preferably made of metal which is a good conductor ofheat. Thus heat radiated from the sheath 22 in the region of the weld iscarried away by the metal of the tube 44 toward the outer end of thetube and such heat is also conducted through the metal of the tube 44into the oil flowing through the tube to further dissipate heat andreduce the amount of heat that reaches the cable core during the weldingoperation. Thus the tube 44 serves the additional function of heatshield for the cable core in the region of the weld ing operation bywhich the joint housing is connected to the cable sheath.

After the weld 40 has cooled, the tube 44 is pulled back out of theclearance between the sheath 22 and the cable core. If the sealingelement 50 is tightly wedged, the wedge surface 48 pulls part way out ofthe sealing element 50 and permits the sealing element to contract sothat it has little or no friction with the sheath and can be removedwith the tube 44. Oil is then free to circulate through the entireannular cross-section of the clearance between the sheath 22 and thecable core and to flow into the joint housing 36.

Joint housings are made in sections and another section of the jointhousing 36 may be connected to another cable which is to be joined inthe housing to the cable shown in FIG. 1. This other section of thejoint housing can be connected to the other cable in the same way asalready described in connection with FIG. 1. After connections betweenthe cables have been made, the different parts of the joint housing areassembled and joined together, but this isconventional and forms no partof the present invention.

The preferred embodiment of the invention has been illustrated anddescribed, but changes and modifications can be made and some featurescan be used in different combinations without departing from theinvention as defined in the claims.

What is claimed is:

l. A construction on an end of an oil-filled cable, that has insulatedconductors assembled in a core of the cable and an oil-tight sheathsurrounding the cable core with clearance space, and insulating oilaround the core, a tube fitting over an end portion of the core andextending forward for some distance into the clearance space between thecore and the inside surface of the sheath, sealing means on the tube inposition to prevent the oil in the sheath from running beyond thesealing means through the clearance space between the tube and sheath ina direction toward the end of the sheath, and the outer end of the tuberemote from the sealing means being beyond said end of the sheathwhereby oil passes between the tube and the cable beyond the seal ingmeans but the space between the outside of the tube and the inside ofthe sheath is empty so long as the end of the sheath is free to drain.

2. The construction described in claim 1 characterized by the sheathbeing made of metal, and a metal connector housing into which the endportion of the sheath extends for a distance that locates the end of thehousing over the sheath between the axial location of the sealing meansand the end of the sheath, said end of the housing being connected tothe sheath by welding.

3. The construction described in claim 1 characterized by the core ofthe cable having oil channels therein for circulation of oil in thecable including circulation longitudinally of the cable and through thetube and out through the end of the tube remote from the sealing means.

4. The construction described in claim 1 characterized by the sealingmeans including a ring of heat resistant elastomer surrounding theoutside of the forward portion of the tube, and the tube having acircumferential ridge projecting upward to increase its diameter nearthe forward portion but behind the sealing ring for holding the ringagainst axial movement as the construction is assembled by pushing thetube into the space between the core and the sheath of the cable.

5. The construction described in claim 4 characterized by the ridgehaving a sloping face on its forward side and over which the ring islocated. said sloping face serving as a wedge for thrusting the ringinto contact with the inside surface of the sheath.

6. The construction described in claim 5 characterized by the tube beingof one-piece construction around its full circumference and being aloose fit on the core and being made of metal and a good conductor ofheat for carrying away heat by conduction from a region rearward of theride where heat is applied to the outside of the sheath to fuse it to aconnector housing, the ridge being of integral construction with thetube, and the ring being a sleeve of greater axial length thanthickness, and surrounding the ridge with the rearward edge of thesleeve extending radially beyond the radial limits of the ridge and intosealing contact with the inside surface of the sheath.

7. The construction described in claim 5 characterized by meanssupplying oil to the inside of the sheath at a distance upstream fromthe end of the sheath at which the tube is located, and a pump connectedto said oil supplying means for maintaining pressure on the oil in thecable and for maintaining a flow of oil out through the tube duringwelding of a housing to the sheath.

8. The method of fusion connecting an end portion of a sheath of an oilfilled cable to a joint housing, comprising the steps of surrounding acore of the cable with an oil impervious tube that extends from alocation beyond the end of the sheath and into a space between the coreof the cable and the end portion of the sheath that surrounds the corewith some clearance between the core and the sheath, sealing anyclearance between sheath and the forward portion of the tube, andconnecting a housing to the end portion of the sheath by a fusionbonding at a region located axially between the region of sealing andthe adjacent end of the sheath while said sealing prevents oil in thecable from entering the space between the outside of the tube and theinside surface of the sheath.

9. The method described in claim 8 characterized by keeping the sheath,ahead of the sealing location, and the insulation of the cable, filledwith oil during the bonding of the sheath to the housing, andmaintaining a superatmospheric pressure on the oil in the cable duringfusion bonding so that flow of oil through the cable in the tubedischarges from the end of the cable beyond the region of fusion bondingand carries away heat from the region of fusion bonding, and removingthe tube from the core after the fusion bonding step.

10. The method described in claim 8 characterized by welding the sheathto the housing as the fusion bonding, using a stiff metal tube as thetube that fits into the sheath and loosely around the core to surroundthe core, and effecting said sealing of any clearance portion of thetube between the forward portion of the tube and the inside surface ofthe sheath by forcing a wedge-shaped element of the tube into saidclearance.

1. A construction on an end of an oil-filled cable, that has insulatedconductors assembled in a core of the cable and an oiltight sheathsurrounding the cable core with clearance space, and insulating oilaround the core, a tube fitting over an end portion of the core andextending forward for some distance into the clearance space between thecore and the inside surface of the sheath, sealing means on the tube inposition to prevent the oil in the sheath from running beyond thesealing means through the clearance space between the tube and sheath ina direction toward the end of the sheath, and the outer end of the tuberemote from the sealing means being beyond said end of the sheathwhereby oil passes between the tube and the cable beyond the sealingmeans but the space between the outside of the tube and the inside ofthe sheath is empty so long as the end of the sheath is free to drain.2. The construction described in claim 1 characterized by the sheathbeing made of metal, and a metal connector housing into which the endportion of the sheath extends for a distance that locates the end of thehousing over the sheath between the axial location of the sealing meansand the end of the sheath, said end of the housing being connected tothe sheath by welding.
 3. The construction described in claim 1characterized by the core of the cable having oil channels therein forcirculation of oil in the cable including circulation longitudinally ofthe cable and through the tube and out through the end of the tuberemote from the sealing means.
 4. The construction described in claim 1characterized by the sealing means including a ring of heat resistantelastomer surrounding the outside of the forward portion of the tube,and the tube having a circumferential ridge projecting upward toincrease its diameter near the forward portion but behind the sealingring for holding the ring against axial movement as the construction isassembled by pushing the tube into the space between the core and thesheath of the cable.
 5. The construction described in claim 4characterized by the ridge having a sloping face on its forward side andover which the ring is located, said sloping face serving as a wedge forthrusting the ring into contact with the inside surface of the sheath.6. The construction described in claim 5 characterized by the tube beingof one-piece construction around its full circumference and being aloose fit on the core and being made of metal and a good conductor ofheat for carrying away heat by conduction from a region rearward of theridge where heat is applied to the outside of the sheath to fuse it to aconnector housing, the ridge being of integral construction with thetube, and the ring being a sleeve of greater axial length thanthickness, and surrounding the ridge with the rearward edge of thesleeve extending radially beyond the radial limits of the ridge and intosealing contact with the inside surface of the sheath.
 7. Theconstruction described in claim 5 characterized by means supplying oilto the inside of the sheath at a distance upstream from the end of thesheath at which the tube is located, and a pump connected to said oilsupplying means for maintaining pressure on the oil in the cable and formaintaining a flow of oil out through the tube during welding of ahousing to the sheath.
 8. The method of fusion connecting an end portionof a sheath of an oil filled cable to a joint housing, comprising thesteps of surrounding a core of the cable with an oil impervious tubethat extends from a location beyond the end of the sheath and into aspace between the core of the cable and the end portion of the sheaththat surrounds the core with some clearance between the core and thesheath, sealing any clearance between sheath and the forward portion ofthe tube, and connecting a housing to the end portion of the sheath by afusion bonding at a region located axially between the region of sealingand the adjacent end of the sheath while said sealing prevents oil inthe cable from entering the space between the outside of the tube andthe inside surface of the sheath.
 9. The method described in claim 8characterized by keeping the sheath, ahead of the sealing location, andthe insulation of the cable, filled with oil during the bonding of thesheath to the housing, and maintaining a superatmospheric pressure onthe oil in the cable during fusion bonding so that flow of oil throughthe cable in the tube discharges from the end of the cable beyond theRegion of fusion bonding and carries away heat from the region of fusionbonding, and removing the tube from the core after the fusion bondingstep.
 10. The method described in claim 8 characterized by welding thesheath to the housing as the fusion bonding, using a stiff metal tube asthe tube that fits into the sheath and loosely around the core tosurround the core, and effecting said sealing of any clearance portionof the tube between the forward portion of the tube and the insidesurface of the sheath by forcing a wedge-shaped element of the tube intosaid clearance.